Hypothesis / aims of study
Clinical practice for overactive bladder (OAB) has been expanding since the introduction of OAB definition based on “urgency” symptom. On the other hand, there are not yet universally accepted definition of underactive bladder (UAB) reflecting the urodynamic observation of detrusor underactivity (DUA). Many studies have attempted to determine the definition of UAB or to evaluate DUA without invasive urodynamics. Uroflowmetry (UFM) is a non-invasive urodynamic examination to evaluate voiding condition. A wide variety of curve pattern on UFM is traced depending on a condition of detrusor contractility and outlet obstruction. However, there is no internationally accepted definition of how to interpret UFM curve pattern in adults. The ICS terminology only mentions continuous and intermittent pattern on UFM [1]. A recent literature showed that the sawtooth and interrupted pattern on UFM was strongly correlated with DUA diagnosed by invasive urodynamics [2]. They reported that 80% of patients with DUA without bladder outlet obstruction (BOO) represented the sawtooth and interrupted patterns while only 12.8% of patients with BOO without DUA did. If this pattern is reproducible, the UFM curve patterns could help to determine DUA. In this study, we investigated if the UFM curve patterns represented DUA or BOO.
Study design, materials and methods
According to the statistical calculation based on the previous report, we estimated that the data of 15 patients in each group (i.e., Group 1: BOO without DUA and Group 2: DUA without BOO) would be needed to confirm the occurrence rate of sawtooth and interrupted pattern. Thus, we retrospectively collected 100 consecutive data of male patients who were evaluated using UFM and invasive urodynamics (pressure-flow study). DUA and BOO were diagnosed according to bladder contractility index (BCI) and BOO index (BOOI). DUA and BOO were defined as BCI ≤100 and BOOI >40, respectively. The UFM curve with 2 or more notches was defined as sawtooth pattern and the interrupted pattern was defined if several curves with interruptions reducing to zero were noted (Figure). The occurrence rate of these patterns was compared between the 2 groups. We also compared other UFM parameters including maximum and average flow rate (Qmax and Qave), postvoid residual (PVR), voiding time (VT), time to Qmax, Qmax and Qave corrected by voided volume (cQmax and cQave), the slope to 1st peak flow, the number of notches on the curve (sawtooth pattern), the number of curves (interrupted pattern) and the maximum drop on the sawtooth pattern (Figure).
Results
Among the 100 consecutive male patients, 25 patients in Group 1 and 49 in Group 2 were collected. The sawtooth pattern was observed in 8 patients (32%) in Group 1 and 28 (57%) in group 2 with a significant difference between the 2 groups. The interrupted pattern was observed in 9 (36%) and 24 (49%), and the both patterns was observed in 5 (20%) and 14 (29%), respectively, without significant difference. Among the other parameters, there were significant differences in age, prostatic volume (PV), the slope to 1st peak flow, the number of notches on the curve and the maximum drop between the 2 groups (Table). The area under the curve (AUC) of each significant parameter on ROC curve was 0.75 (age), 0.67 (PV), 0.58 (the slope to 1st peak flow), 0.61 (the number of notches), and 0.76 (the maximum drop), respectively (Table).
Interpretation of results
The sawtooth pattern was more frequently observed in patients with DUA than in those with BOO. This is consistent with the previous study [2]. However, in the present study, the sawtooth pattern was observed in as much as 32% of the patients with BOO. The occurrence rate of the interrupted pattern was similar in the 2 groups. Thus, compared with the previous study, the differences detected in these UFM patterns between the 2 groups were subtle in the present study.
Qmax, Qave or VT that are automatically analyzed parameters on UFM were not significantly different between the 2 groups. The new UFM parameters such as the slope to 1st peak flow, the number of notches and the maximum drop might help to distinguish DUA from BOO.